Question $(2)(5\mathrm{.}0$ points$)$

It is required to design the pavement for an access highway to a major truck terminal. The design daily truck traffic consists of the following:

$75$ single axles at $24,000lb$ each, $580$ tandem axles at $26,000lb$ each, $55$ tandem axles at $40,000lb$ each, and $75$ triple axles at $46,000lb$ each.

The highway is to be designed with rigid pavement having a modulus of rupture of $500l\frac{b}{i}{n}^2$nd a modulus of elasticity of $4$ million $l\frac{b}{i}{n}^2.$ The reliability is to be $95\%,$ the overall standard deviation is $0\mathrm{.}45,$ the drainage coefficient is $0\mathrm{.}9\frac{,}{{?}_{\frac{?}{?}}}\frac{?}{\text{P}\text{S}\text{I}}$ is $1\mathrm{.}8($with a TSI of $2\mathrm{.}5),$ and the load transfer coefficient is $3\mathrm{.}3.$ The modulus of subgrade reaction is $300l\frac{b}{i}{n}^3.$ If a $20-$year design life is to be used, determine the required slab thickness. $($Written answer only please$)$